Interactive devices are commonly used in conjunction with displays for interfacing purposes. For example, pointing devices commonly known as pointers are often used as presentation tools in classes, lectures, and meetings. A pointer may emit a bright mark onto a screen, thus illuminating a particular point or area of interest on the displayed image or document, and aiding in clarifying the presenter's discussion.
As another example, the pointing device known as a mouse is commonly used with the modern computer system. A mouse functions by detecting two-dimensional motion relative to its supporting surface. A screen cursor, corresponding to the movement of the mouse, is displayed on the screen, so as to aid the user in ascertaining the intended position and direction of movement on the screen. A user may navigate the cursor using the mouse, and select or maneuver screen objects via activating one or more buttons on the mouse.
As a further example, in the world of video gaming, the use of a pointing device has become a common method of interfacing between a video game player and the game environment. A popular pointing device is known as the light gun, many variations of which have been produced. A typical light gun contains a gun-shaped housing with a trigger, which a user may point and shoot toward an on-screen target. The game system then determines whether the target was hit or missed by the shot, and may display an on-screen response accordingly.
Traditionally, light guns were designed for use with cathode ray tube (CRT) monitors. In operation, an image on a CRT monitor is “painted” by a scanning electron beam moving across the screen on a horizontal line from left to right, and line by line from top to bottom. Upon reaching the right end of a line, the beam must move back to the left and down one line in order to begin painting the next horizontal line. The movement back to the left side of the next line is referred to as a “horizontal retrace.” Upon reaching the right end of the bottom line, the beam must move back up to the upper left corner of the screen to begin another trace pattern. This movement back to the upper left is referred to as a “vertical retrace.” Similarly, a “horizontal retrace signal” or “vertical retrace signal” instructs the system to move the beam back to the left of the next line, or upper left corner, respectively. The screen image as a whole appears instantaneously to the human eye as a result of visual persistence of the eye, since the movement is performed very quickly.
When a user pulls the trigger of a light gun, the system may employ either of two methods to ascertain whether the gun is aimed at the target. Upon the trigger being activated, the computer connected to the gun is notified and blanks the CRT screen to black. At this point, the gun begins receiving light through a photodiode in its barrel. A first method entails painting the target object white. If the photodiode senses darkness after one vertical retrace signal, followed by light after the next, the computer recognizes this pattern to indicate a hit target. In a second method, the entire screen and not just the target is painted white. By relating the photodiode signal with the horizontal and vertical retrace signals, the computer determines the location on the screen at which the gun is pointed when its photodiode first senses light (i.e., when the trigger is pulled).
The traditional light gun described above is thus operable as a game interfacing device only when CRT screens are used. Users, however, may wish to use various types of screens such as LCD, plasma, or other displays. Indeed, many forms of television and computer monitors that employ simultaneous refreshing of pixels, and thus no retracing, have become popular in recent years. The traditional light gun thus cannot be used with these monitors, since the display timing method of tracking a target, as described above, is irrelevant outside the context of traditional CRT beam-scanning.
An alternative method of gun interfacing, such as that used in the Nintendo Wii, entails the use of a separate light-emitting apparatus placed, for example, near or adjacent to the display screen. The apparatus emits light to be received by a sensor in the gun, while a user aiming the gun toward the screen pulls the gun trigger. The light-emitting apparatus may be formed as a bar on which lights are placed at both ends. Prior to game play, the user must calibrate the system to recognize the screen position at which the user is pointing, relative to the various lights on the light-emitting apparatus. During game play, a method such as triangulation may then be used to calculate the user's position with respect to the screen.
Although the method above may be compatible with non-CRT screens, certain drawbacks can occur. For example, the necessity of a light-emitting bar inevitably entails a limited viewing (pointing) angle for the gun sensor. In addition, the use of this additional piece of hardware requires a more complicated setup process, including the mounting, positioning, and calibration of the bar. The required calibration may also lend to some difficulty in maintaining accuracy should a user decide to drastically change default positions.
Another method employs a tracking camera placed above the screen. The camera keeps track of two light sources on the gun itself. In this method as well, the system must be re-calibrated to maintain accuracy when the user changes his shooting position, distance, or style.
Hence, it is desirable to have a solution without the above-described disadvantages. As will be seen, the invention provides such a solution in an elegant manner.